away with the fairies

adjective3

1. •
   Not all there; slightly crazy.

   • Now, I know the story is away with the fairies, but he produces a body and I take him down to the station to talk to the detectives. — 2000
2. •
   Synonym of lost in thought; distracted or daydreaming.

   • Goodness, you were away with the fairies then! Did you hear me? I asked if you wanted another cup of tea? — 2012
3. •
   Fast asleep.